<template>    <div >        <div class="a">            <button @click="testClick">改变 a 值</button>            <div class="b">                <span> 这是 a 值 ： {{a}}</span>            </div>        </div>        <List></List>    </div></template><script>    import List from './components/List.vue'    import Counper from './components/Counper.vue'export default{    data : function(){        return {            a : 1        }    },    components : {        List,        Counper    },    methods : {        testClick(){            this.a = Math.random()        }    }}</script><style scoped>.a{    background: indianred;}    .b{        background: deepskyblue;    }</style>